[PATCH 24/74] union-mount: Introduce MNT_UNION and MS_UNION flags

[Valerie Aurora <valerie.aurora@gmail.com>]

From: Jan Blunck <jblunck@suse.de>

Add per mountpoint flag for Union Mount support. You need additional patches
to util-linux for that to work - see:

git://git.kernel.org/pub/scm/utils/util-linux-ng/val/util-linux-ng.git

Signed-off-by: Jan Blunck <jblunck@suse.de>
Signed-off-by: Valerie Aurora <vaurora@redhat.com>
Signed-off-by: Valerie Aurora <valerie.aurora@gmail.com>
---
 fs/namespace.c        |    5 ++++-
 include/linux/fs.h    |    1 +
 include/linux/mount.h |    1 +
 3 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 0f028e0..054eb7d 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -862,6 +862,7 @@ static void show_mnt_opts(struct seq_file *m, struct vfsmount *mnt)
 		{ MNT_NOATIME, ",noatime" },
 		{ MNT_NODIRATIME, ",nodiratime" },
 		{ MNT_RELATIME, ",relatime" },
+		{ MNT_UNION, ",union" },
 		{ 0, NULL }
 	};
 	const struct proc_fs_info *fs_infop;
@@ -2095,10 +2096,12 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
 		mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
 	if (flags & MS_RDONLY)
 		mnt_flags |= MNT_READONLY;
+	if (flags & MS_UNION)
+		mnt_flags |= MNT_UNION;
 
 	flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN |
 		   MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT |
-		   MS_STRICTATIME);
+		   MS_STRICTATIME | MS_UNION);
 
 	if (flags & MS_REMOUNT)
 		retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags,
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 469e0ea..dad9903 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -191,6 +191,7 @@ struct inodes_stat_t {
 #define MS_REMOUNT	32	/* Alter flags of a mounted FS */
 #define MS_MANDLOCK	64	/* Allow mandatory locks on an FS */
 #define MS_DIRSYNC	128	/* Directory modifications are synchronous */
+#define MS_UNION	256	/* Merge namespace with FS mounted below */
 #define MS_NOATIME	1024	/* Do not update access times. */
 #define MS_NODIRATIME	2048	/* Do not update directory access times */
 #define MS_BIND		4096
diff --git a/include/linux/mount.h b/include/linux/mount.h
index 44aa119..1c69bee 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -46,6 +46,7 @@ struct mnt_namespace;
 
 #define MNT_INTERNAL	0x4000
 #define MNT_HARD_READONLY	0x8000	/* has a hard read-only ref on the sb */
+#define MNT_UNION	0x10000		/* top layer of a union mount */
 
 struct vfsmount {
 	struct list_head mnt_hash;
-- 
1.7.0.4